1. Field of the Invention
This invention relates to a reference electrode. Particularly this invention relates to a reference electrode which features simplicity of construction, permits miniaturization, and possesses an insensitive film on its electrode surfaces. More particularly, this invention relates to a reference electrode used by a combination with an ion sensor, a pH sensor and so on.
2. Description of Prior Arts
In recent years, the coating on the surface of a conductor with a film for the purpose of conferring a new potentiality upon the conductor has come to prevail. The electrode coated with such a film is generally called a "polymer coated electrode." The polymer coated electrode shows a promise in potential application to electrocatalysis, transducers, analytical sensors and so on. To exploit such a novel function, the polymer coated electrode dictates payment of due consideration to electroconductivity and other various properties to be displayed by the coating film directly applied to the surface of the electrode. In the case of an electrode to be used for an ion sensor or a pH sensor, for example, the coating film is required to possess selective permeability to a particular ion species desired to be detected.
Heretofore, a saturated calomel electrode and a silver/silver chloride electrode have been chiefly used as a reference electrode.
A reference electrode is required to possess a room for holding the saturated sodium chloride (NaCl) solution into which Hg/Hg.sub.2 Cl.sub.2 or Ag/AgCl is dipped. The reference solution of the saturated NaCl and a test solution is connected each other across a thin glass filter. When such a reference electrode is to be miniaturized or to be used in the field of medical inspection, since the reference electrode is furnished a room of reference solution, there is the possibility that a test solution under measurement mingles with the reference solution or the inner reference solution leaks owing to change in the temperature of the solution under measurement. Besides, the reference solution itself becomes a serious obstacle to fabricate the electrode in a miniaturized design. Thus, various difficulties are inevitably encountered. As a solution of these problems occuring from a reference solution, we have filed Japanese Patent Application No. 206095/1981, covering an invention relating to a reference electrode having at least one polymer film (a film of the polymer derived from a hydroxy-aromatic compound) directly coated either on the surface of a conductor (chiefly of silver) or on the surface of a layer of a halide (chiefly silver halide) deposited on a conductor. Since this reference electrode has been prepared simply by coating the surface of a conductor with a polymer film, it does not require incorporation of any room of a reference solution and can be miniaturized to the limit imposed only by the fabricability of the conductor. In general, the deposition of the polymer film on the conductor is effected chiefly by the electrochemical oxidation polymerization technique, enabling the surface of the conductor to be directly coated with the film.